Two Layer Pavement Preservation System

ABSTRACT

A pavement preservation system comprises two layers of specialized chip seal applications. The first layer is a Polymer Modified Asphalt Rubber chip seal application. This layer is composed of an application of Polymer Modified Asphalt Rubber binder followed by a hot pre-coated ⅜ or ½ inch aggregate placed at 28 to 34 pounds per square yard and rolled into the binder material. The second layer is a Rubberized Asphalt Binder chip seal application. This layer is composed of an application of Rubberized Asphalt Binder followed by a hot pre-coated ⅛ inch aggregate placed at 10 to 14 pounds per square yard and rolled into the binder material.

CROSS REFERENCE TO RELATED APPLICATION

This Application claims the benefit of U.S. Provisional PatentApplication No. 61/251,725, filed on Oct. 14, 2010.

BACKGROUND OF THE INVENTION

Flexible pavement roadways, such as those made of asphalt cementmixtures, usually require periodic surface treatment so the pavementsystem, which deteriorates under wear and weathering, may successfullyachieve its design life. Chip seals are a common preventive maintenancetreatment for both low-volume and high-volume pavements.

A chip seal is essentially a single layer of asphalt binder that iscovered by embedded aggregate (one stone thick), with its primarypurpose being to seal the fine cracks in the underlying pavement'ssurface and prevent water intrusion into the base and subgrade. Theaggregate protects the asphalt layer from damage and combines with theasphalt to develop a macrotexture that results in a skid-resistantsurface for vehicles. Chip seals are expected to provide about 5 yearsof service.

BRIEF SUMMARY OF THE INVENTION

The present invention comprises two layers of specialized chip sealapplications, resulting in a unique two layer system that has specificphysical advantages and improved binder properties. The combination ofthe physical aggregate interlock and highly modified binder materialsresults in a high performance pavement preservation system that can beutilized to rehabilitate badly deteriorated pavements at very low costcompared to the alternative, and at the same time reduce maintenancecosts along with extending service life, allowing for significantimprovements in life cycle costs.

The first layer of the inventive system is a Polymer Modified AsphaltRubber chip seal application. This layer is composed of an applicationof Polymer Modified Asphalt Rubber binder at a rate of about 0.60 to0.70 gallons per square yard. The actual application rate is projectspecific and is determined by the existing pavement condition after theproper pre-maintenance (crack sealing and patching) has been done.Immediately following the application of the Polymer Modified AsphaltRubber binder a hot pre-coated ⅜ or ½ inch aggregate is placed at 28 to34 pounds per square yard and rolled into the binder material. Once therolling is complete and this first layer has had sufficient cure timethe loose aggregate is removed and the Polymer Modified Asphalt Rubberchip seal is ready to receive the second layer of the inventive system.

The second layer of the inventive system is a Rubberized Asphalt Binderchip seal application. This layer is composed of an application ofRubberized Asphalt Binder at a rate of 0.20 to 0.23 gallons per squareyard. Immediately following the application of the Rubberized AsphaltBinder a hot pre-coated ⅛ inch aggregate is placed at 10 to 14 poundsper square yard and rolled into the binder material. Once the rolling iscomplete and this second layer has had sufficient cure time the looseaggregate is removed and the Two Layer Pavement Preservation System iscomplete in place.

Aspects and applications of the invention presented here are describedbelow in the drawings and detailed description of the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a cross section of deteriorated pavement with a first layerof the inventive system applied.

FIG. 2 shows the pavement cross section of FIG. 1 with both layers ofthe inventive system applied.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, and for the purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the various aspects of the invention. It will beunderstood, however, by those skilled in the relevant arts, that thepresent invention may be practiced without these specific details. Inother instances, known structures and devices are shown or discussedmore generally in order to avoid obscuring the invention.

The inventive system comprises a bituminous surface Stress AbsorbingMembrane Interlayer (SAMI) composed of a single application of PolymerModified Asphalt-Rubber material and pre-coated aggregate (first layer)followed by a second bituminous surface Stress Absorbing Membrane (SAM)composed of a single application of Rubberized Asphalt Binder andpre-coated aggregate (second layer) in accordance with the followingspecification. Pre-maintenance (crack sealing and patching) of theexisting pavement surface may be desirable, depending upon the localconditions.

Material Components

PG Asphalt Cement. The type and grade of PG (Performance Graded) asphaltcement utilized to manufacture the Polymer Modified Asphalt Rubberbinder and Rubberized Asphalt Binder will be PG 64-16, PG 58-22 or PG58-28 which should comply with requirements in Table #1.

TABLE #1 PG Asphalt Cement Grading Requirements Climate PG Grading ColdPG 58-28 Moderate and Hot PG 64-16 or PG 58-22

Granulated Reclaimed Tire Rubber. The CRM (Crumb Rubber Modifier) shouldbe produced primarily from the processing of whole automobile and trucktires. The rubber should be produced by ambient temperature grindingprocesses only. The SBS (styrene butadiene styrene) polymer should be alinear or radial type of polymer with a molecular weight sufficientenough to meet the end result physical binder requirements. Thegradation of the CRM and SBS Polymer when tested in accordance with ASTMC-136 (dry sieve only) and using a 100 gram sample, should meet therequirements in Table #2.

TABLE #2 CRM and SBS Polymer Grading Requirements For Second Layer ForFirst Layer Reclaimed Reclaimed Tire (CRM) For Both Layers Tire CRMPercent SBS Polymer Sieve Size Percent Passing Passing Percent Passing #8 (2.36 mm) 100 — Per Binder Manufacturer #10 (2 mm) 95-100 — PerBinder Manufacturer #16 (1.18 mm) 45-75  — Per Binder Manufacturer #20(mm) — 100 Per Binder Manufacturer #30 (600 μm) 2-20 95-100 Per BinderManufacturer #50 (300 μm) 0-10 Open Per Binder Manufacturer #200 (75 μm)— Open Per Binder Manufacturer

The use of CRM from multiple sources is acceptable provided that theoverall blend of rubber meets the gradation requirements. The individualCRM particles, irrespective of diameter, should not be greater in lengththan 3/16 of an inch (5 mm).

The CRM should have a specific gravity of 1.15±0.05, and should be freeof loose fabric, wire and other contaminants except that up to 4 percent(by weight of rubber) calcium carbonate or talc may be added to preventthe rubber particles from sticking together. The rubber should besufficiently dry so as to be free flowing and not produce a foamingproblem when blended with the hot asphalt cement. The Reclaimed Tire CRMmaterial should conform to the chemical analysis in Table #3.

TABLE #3 Reclaimed Tire CRM Chemical Requirements Test ASTM Test MethodMinimum Maximum Acetone Extract D 297  6.0% 16.0% Ash Content D 297 —8.0% Carbon Black Content D 297 28.0% 38.0% Rubber Hydrocarbon D 29742.0% 65.0% Natural Rubber Content D 297 22.0% 39.0%

Polymer Modified Asphalt Rubber Binder and Rubberized Asphalt Binder.The temperature of the blended PG asphalt cement should not be less that375° F. nor more than 450° F. when the CRM and the SBS Polymer arehomogenously blended and/or milled with either binder, in the field. Thecombined materials should be reacted for a minimum of 90 minutes afterthe incorporation of all the CRM and SBS Polymer. The Polymer ModifiedAsphalt Rubber binder and Rubberized Asphalt Binder should meet therequirements in Table #4 and Table #5, when the reaction/interaction iscomplete.

TABLE #4 Specification Limits for Polymer Modified Asphalt Rubber BinderHot Moderate Cold Climate Climate Climate Apparent viscosity, 375° F.Min 1500 1500 1500 (190° C.), cps. Max 3500 3500 3500 (ASTM D2669) or(Rion Viscotester) Cone Penetration, 77° F. (25° C.), Min 15 20 25 150g, 5 sec; 1/10 dm (ASTM D217) Needle Penetration, 39.2° F., Min 15 20 25200 g, 60 sec, dmm (ASTM D5) Softening Point, ° F. (° C.) Min 150° F.145° F. 140° F. (ASTM D36) (66° C.) (63° C.) (60° C.) Resilience, 77° F.(25° C.), % Min 40 30 20 (ASTM D3407)

TABLE #5 Specifications Limits for Rubberized Asphalt Binder Hot &Moderate Cold Climate Climate Rotational Viscosity, 375° F. (190° C.)Min 200 200 (ASTM D2669) or (Rion Viscotester) Max 900 900 NeedlePenetration, 77° F. (25° C.) Min 35 45 100 g/5 sec., dmm (ASTM D5) Max75 95 Softening Point, ° F. (° C.) (ASTM D36) Min 140° F. 130° F. (60°C.) (54° C.) Elastic Recovery @ 77° F. (25° C.), 20 cm Min 55 50elongation, 5 cm/min., % recovery @ 1 hr. Resilience, % rebound (ASTMD5329) Min 20 18 Dynamic Shear, G*/sinδ, kPa (76° C.) Min 1.00 1.00(AASHTO T315) Climate Definitions Hot Climate Average July Max @ 110° F.Average January Low @ 30° F. or above Moderate Climate Average July Max@ 100° F. Average January Low @ 15° F.-30° F. Cold Climate Average JulyMax @ 80° F. Average January Low @ 15° F. or lower

The viscosity test should be conducted by using a hand held HAAKEviscometer (or equal), with rotor 1, 24 mm in depth×53 mm in height, orequivalent. The fully reacted Polymer Modified Asphalt Rubber binder andRubberized Asphalt Binder should be maintained at a temperature of notless than 375° F. nor more than 425° F.

If material in a batch of Polymer Modified Asphalt Rubber binder orRubberized Asphalt Binder is not used within six hours after thereaction period is complete, heating of the material should bediscontinued. When the Polymer Modified Asphalt Rubber binder orRubberized Asphalt Binder temperature cools below 375° F. and is thenreheated, it should be considered a reheat cycle. The total number ofreheat cycles should not exceed two (2). The binder materials should beuniformly reheated to a temperature of not less than 375° F. Additionalscrap tire CRM may be added to the reheated Polymer Modified AsphaltRubber binder and reacted for a minimum of 30 minutes and should notexceed 10 percent of the total binder weight. Reheated Polymer ModifiedAsphalt Rubber binder should conform to the requirements for blendedPolymer Modified Asphalt Rubber binder.

Aggregate Cover Material. Aggregate should be composed of clean anddurable crushed rock or crushed gravel conforming to the followingrequirements:

Proposed aggregate samples should be tested for compatibility andstripping characteristics (vialit testing). The test method is describedbelow.

If the aggregate is to be crushed stone, it should be manufactured fromsound, hard, durable material of accepted quality and crushed tospecification size. All strata, streaks and pockets of clay, dirt,sandstone, soft rock or other unsuitable material accompanying the soundrock should be discarded and not allowed to enter the crusher.

If the aggregate material is to be crushed gravel, it should consist ofhard, durable fragments of stone or gravel of accepted quality andcrushed to specification size. All strata, streaks, pockets of sand,excessively fine gravel, clay or other unsuitable material including allstones, rocks and boulders of inferior quality should be discarded andnot allowed to enter the crusher. The crushing of the gravel shouldseparate the #4, ⅜ and ½ inch sieves and should have a minimum 95% ofthe particles with a minimum of one mechanically fractured face and 90%of the particles should have a minimum of two mechanically fracturedfaces.

The ⅜ inch crushed aggregate or crushed gravel should not contain morethan 8% by weight of flat or elongated pieces and should be free fromwood, roots and vegetable or other organic extraneous matter. The ⅜ inchcrushed aggregate or crushed gravel should have a minimum CleannessValue (CV) of 80, the ⅛ inch crushed aggregate or crushed gravel shouldhave a minimum Cleanness Value (CV) of 88, and should have a percentageof wear not more than 7 percent at 100 revolutions and not more than 30percent at 500 revolutions, as determined by ASTM C131 or CaliforniaTest Method 211. Note: When performing the percentage of wear testingfor the ⅛ inch aggregate Schedule “D” Sizing will be required asindicated in California Test Method 211. Modified Fine Durabilitytesting should also be required for the ⅛ inch aggregate, with a minimumacceptable value at 76, as required by California Test Method 229.

The aggregate should show no evidence of disintegration nor show a totalloss greater than 12% when subjected to 5 cycles of the sodium sulfateaccelerated soundness test specified in ASTM C88.

The crushed aggregate for Polymer Modified Asphalt Rubber binderapplications should meet the requirements for gradation given in Table6. The crushed aggregate for Rubberized Asphalt Binder should meet therequirements for gradation given in Table 7, when tested in accordancewith ASTM C136. The ⅛ inch aggregate should be a porphyritic olivinebasalt with a specific gravity (coarse bulk SSD) ranging from 2.6-2.8,California Test Method 206. Gray or light colored aggregate should notbe used as part of the Rubberized Asphalt Binder chip seal surfacecourse.

TABLE 6 Aggregate Gradation Requirements - Polymer Modified AsphaltRubber Sieve Size Percent Passing ½ inch (12 mm)  95-100 ⅜ inch (9 mm)70-85 ¼ inch (4.75 mm)  0-15 #8 (2.36 mm) 0-5 #200 (75 μm) 0-1 — —

TABLE 7 ⅛^(th) Inch Aggregate Gradation Requirements - RubberizedAsphalt Binder Sieve Size Percent Passing ⅜ inch (9 mm) 100 ¼ inch (4.75mm)  95-100 #8 (2.36 mm) 20-50 #16 (1.18 mm)  0-10 #30 (600 μm) 0-2 #200(75 μm) 0-1

The aggregate to be utilized for both binder materials should be hotpre-coated with 0.5 to 1.0 percent PG asphalt cement. The pre-coatedaggregate should have a “salt and pepper” appearance and supplied to theproject site at 225° F. to 325° F.

There needs to be insurance that good adhesion occurs between binder andaggregate, at the time of placement. The Vialit Retention Test providesa method to assess the active adhesivity of the binder and the aggregatebeing utilized in conditions, which simulate actual project variablesand environment. This method is an indicator of aggregate retention forhot applied chip seal, pavement preservation surface treatments. It is amodification of European Standard EN12272-3, adapted to hot sprayapplied rubberized/polymer chip seal binders.

Vialit Retention Test. Hot applied, modified binder materials areapplied at 79 grams (0.42 gal/sy) to standard size, clean and dry,stainless steel plates. Exactly one hundred (100) washed and gradedaggregate particles are embedded into the required binder type. Thesample is allowed to cure under specified conditions. Following thiscure, the individual plates are conditioned at three differenttemperatures for 30 minutes. Then a 500 gram steel ball is dropped three(3) times from a distance of 50 cm (20 inches) onto the invertedstainless steel plates. The results are recorded at % aggregateretention with 90% retention being the minimum allowable value.

Steps for Modified Test Method

-   -   1) Hot asphalt cement, Polymer Modified Asphalt Rubber or        Rubberized Asphalt Binder is pre-heated to approximate        application temperature 330° F. (165° C.) to 375° F. (190° C.).    -   2a) Tare weight of plate is recorded.    -   2b) Individual plates are pre-heated in an oven to a minimum of        330° F. (165° C.).    -   2c) 79 grams of asphalt cement/modified binder applied to each        plate.    -   2d) Plates are returned to the 330° F. (165° C.) minimum        temperature oven for 15 minutes.    -   2e) Plates are removed from the oven and placed on a warm        hotplate and the binder is spread and smoothed with a hot blade.    -   2f) Application weight is verified and adjusted as needed.    -   2g) 100 particles of washed and graded aggregate, meeting the        project specification requirements, are applied in a 10×10        matrix, with the plate still on the warm hotplate.    -   2h) Three (3) plates are prepared for each combination of binder        and aggregate.    -   3) Plates are again returned to the 330° F. (165° C.) minimum        temperature oven for 15 minutes.    -   4a) Plates are removed from the oven and allowed to cool at room        temperature for four to six hours.    -   4b) Once the room temperature cure is complete, individual        plates are conditioned for 30 minutes at each of the following        temperatures: 41° F. (5° C.), 14° F. (−10° C.) and −8° F. (−22°        C.).    -   5) After the 500 gram steel ball has been dropped three times on        each of the three samples, report the number of stones attached        as percent aggregate retention at test temperature.

Equipment

Primary equipment utilized in the production and application of PolymerModified Asphalt Rubber binder and Rubberized Asphalt Binder materialsis as follows:

A PG asphalt cement heating tank with a hot oil heat transfer system ora retort heating system capable of heating the PG asphalt cement to theproper temperature for blending/milling with the CRM and SBS Polymer.

A Polymer Modified Asphalt Rubber/Rubberized Asphalt Binder mechanicalblender and a Supraton 549-5.03 mill (or equal) should have a two stagecontinuous mixing process capable of producing a homogenous blend of PGasphalt cement CRM and SBS Polymer, at the mix design specified ratios,as directed by the engineer. The mechanical blender should be equippedwith a dual hopper granulated rubber feed system capable of supplyingthe PG asphalt cement feed system, as not to interrupt the continuity ofthe blending process. The maximum capacity of the primary blendingvessel should be 500 gallons. Both the primary and secondary blendersshould be equipped with an agitation device orientated horizontally inthe blending vessel. The mechanical blender and Supraton 549-5.03 millshould be capable of fully blending or milling the individual modifierparticles (CRM and SBS Polymer) with the PG asphalt cement. A separatePG asphalt cement feed pump and finished product pump are required. Thisunit should have a PG asphalt cement totalizing meter in gallons and aflow rate meter in gallons per minute.

A distributor truck equipped with a heating unit, and an internal mixingdevice capable of maintaining a uniform mixture of PG asphalt cement,CRM and SBS Polymer. It should be equipped with a full circulatingspreader bar and pumping system capable of applying the Polymer ModifiedAsphalt Rubber binder and Rubberized Asphalt Binder material within a 1%tolerance of the specified application rate, and must achieve a uniformcovering of the surface to be treated. The distributor should have aboot board on the rear of the vehicle and a bootman should accompany thedistributor. The bootman should ride in a position so that all the spraybar tips are in full view and readily assessable for unplugging, if aplugged tip should occur. The distributor truck should also require athermometer and a computer rate control (CRC) interlinked with aCoriolis Flow Measuring System to ensure and confirm binder applicationrate accuracy.

The cover material (chip) spreader should be a self-propelled machinewith an aggregate receiving hopper in the rear, belt conveyors to carrythe pre-coated aggregate to the front, and a full width spreadinghopper. The spreader should be in good mechanical condition and shouldbe capable of applying the cover aggregate uniformly across the spreadwidth and at the specified application rate, and heat-treated beltsshould be installed on the chip spreader. A minimum of three continuallyoperated self-propelled pneumatic-tired rollers (and one steel wheelroller) should be used for the required rolling of the cover material.The pneumatic-tired rollers' should carry a minimum loading of 3,000pounds on each wheel and a minimum pressure of 90 pounds per square inchin each tire. Foam filled tires can be utilized.

Construction Methods

Immediately prior to the application of the Polymer Modified AsphaltRubber binder and Rubberized Asphalt Binder chip seal applications, thesurface should be clean in order to insure adequate adhesion of thePolymer Modified Asphalt Rubber to the existing pavement surface and theRubberized Asphalt Binder chip seal to the Polymer Modified AsphaltRubber chip seal. Polymer Modified Asphalt Rubber binder and RubberizedAsphalt Binder material should be applied only when the existing surfaceis dry and the atmospheric temperature is above 60° F. and rising.

Concerning the Polymer Modified Asphalt Rubber binder, the percentage ofReclaimed Tire Rubber CRM should be 15-18 percent by weight of the totalPolymer Modified Asphalt Rubber mixture; the exact CRM content should bedetermined by the binder design submitted by the Polymer ModifiedAsphalt Rubber supplier. During Polymer Modified Asphalt Rubber bindermanufacture the CRM percentage should not fluctuate by more than 1 (one)percent by weight of total Polymer Modified Asphalt Rubber mixture, asdetermined by the original laboratory binder design. The SBS Polymershould be 2 percent by weight of the Polymer Modified Asphalt Rubbermixture. Concerning the Rubberized Asphalt Binder, the percentage ofReclaimed Tire Rubber CRM should be 5-10 percent by weight of the totalRubberized Asphalt Binder mixture, the exact CRM content should bedetermined by the binder design submitted by the Rubberized AsphaltBinder supplier. The SBS Polymer should be 2-4 percent by weight of thetotal Rubberized Asphalt Binder mixture. During Rubberized AsphaltBinder manufacture the CRM percentage should not fluctuate by more than1 (one) percent by weight of total Rubberized Asphalt Binder mixture, asdetermined by the laboratory binder design.

The temperature of the PG asphalt cement should be between 375° F. and450° F. at the addition of the CRM and SBS Polymer. The PG asphaltcement, CRM and SBS Polymer should be combined and mixed together in thePolymer Modified Asphalt Rubber binder/Rubberized Asphalt Binderblending unit and/or field Supraton Mill, and reacted in the distributortruck or a reaction vessel for a minimum period of 90 minutes from thetime the CRM and SBS Polymer are blended with the PG asphalt cement. Thetemperature of the Polymer Modified Asphalt Rubber binder and RubberizedAsphalt Binder mixture should be above 375° F. during the reactionperiod, but should not exceed 425° F. at any time.

When a job delay occurs after full reaction, the Polymer ModifiedAsphalt Rubber binder and Rubberized Asphalt Binder may be allowed tocool. The Polymer Modified Asphalt Rubber binder or Rubberized AsphaltBinder should be re-heated slowly just prior to application to atemperature between 375° F. and 400° F. An additional quantity of PGasphalt cement and/or CRM may be added to only to the Polymer ModifiedAsphalt Rubber binder as required to produce a material with theappropriate viscosity.

Placement of the Polymer Modified Asphalt Rubber and Rubberized AsphaltBinder should proceed only under the following conditions: The pavementsurface temperature should be 60° F. and rising. The pavement surface isclean and dry. The wind conditions do not exceed 20 mph. All of theconstruction equipment such as the Polymer Modified AsphaltRubber/Rubberized Asphalt Binder distributor, aggregate spreader, haultrucks loaded with cover material, rollers and brooms are in positionand ready to commence placement operations. Chance of rain does notexceed 75%.

The Polymer Modified Asphalt Rubber binder should be applied to theexisting roadway immediately following mixing and reaction, at atemperature of 375° F. to 400° F. at a rate of 0.60 to 0.65 gallons persquare yard, with a maximum of 1% application rate variance allowed. TheRubberized Asphalt Binder should be applied to the Polymer ModifiedAsphalt Rubber chip seal surface immediately following mixing andreaction, at a temperature of 375° F. to 400° F. at a rate of 0.23 to0.27 gallons per square yard, with a maximum of 1% application ratevariance allowed.

Transverse joints should be constructed by placing building paper acrossand over the end of the previous Polymer Modified Asphalt Rubber binderor Rubberized Asphalt Binder chip seal application. Once the applicationhas progressed beyond the paper, the paper should be removed immediatelyand disposed of. The use of paper may be discontinued if the contractorchooses to squeegee the excess Polymer Modified Asphalt Rubber bindermaterial at the transverse joints prior to the placement of the coveraggregate. All longitudinal joints should not exceed a 12-inches (30 cm)overlap and should be staggered from initial Polymer Modified AsphaltRubber and Rubberized Asphalt Binder application. At no time should thecontractor be allowed to place longitudinal joints one on top of theother.

The ⅜ inch or ½ inch pre-coated aggregate should be applied immediatelyonto the Polymer Modified Asphalt Rubber membrane at a rate of 26 to 34pounds per square yard and the ⅛ inch pre-coated aggregate should beapplied immediately to the Rubberized Asphalt Binder, at a rate of 8 to12 pounds per square yard. The actual rate selected within this rangewill be determined in the field based on the appearance of the PolymerModified Asphalt Rubber chip seal and the Rubberized Asphalt Binder chipseal after initial rolling. At all times the application rate of thecover aggregate should be kept to a minimum. At the time of applicationthe temperature of the aggregate should range from 225° F. to 325° F.

At least three operational pneumatic-tired rollers (and one steel wheelroller) should be provided to accomplish the required embedment of theaggregate cover material. At some project locations, or when productionrates dictate, additional or fewer rollers may be utilized. Thepneumatic tire rollers should be operated in front of the steel wheelroller. There should always be at least 3 (three) operationalpneumatic-tired rollers and 1 (one) 12 to 14 ton operational steel wheelroller on a project. Sufficient rollers should be used for the initialrolling to cover the width of the aggregate spread with one pass. Thefirst pass should be made immediately behind the cover material spreader(chip-box) as the aggregate is being placed. If the spreading is stoppedfor an extended period, the cover material spreader (chip-box) should bemoved ahead or off the chip seal surface so that all cover material maybe immediately rolled. Three complete passes with rollers should be madewith the pneumatic rollers and one pass with the steel wheel roller.

Upon completion of the Polymer Modified Asphalt Rubber chip sealtreatment, the pavement cross section should look as in FIG. 1.Aggregate pieces are embedded in the asphalt binder matrix. Uponcompletion of the Rubberized Asphalt Binder chip seal treatment, thepavement cross section should look as in FIG. 2. Aggregate pieces areembedded in the upper asphalt binder matrix, sitting over the firsttreatment layer.

The foregoing description has been presented and is intended for thepurposes of illustration and description. It is not intended to beexhaustive nor limit the invention to the above teachings. Theembodiments were chosen and described in order to best explain theprinciples of the invention and its practical application and to enableothers skilled in the art to best utilize the invention in variousembodiments and with various modifications as are suited to theparticular use contemplated. Therefore, it is intended that theinvention not be limited to the particular embodiments disclosed forcarrying out the invention

1. A method for installing a dual layer pavement preservation system,comprising the steps of preparing the pavement to receive an asphaltsurface; applying a layer of hot polymer modified asphalt rubber binder;applying a layer of ⅜ inch or ½ inch aggregate that is hot pre-coatedwith 0.5 to 1.0 percent asphalt cement; rolling the aggregate into thebinder material; allowing the combined binder and aggregate to cure;removing any loose aggregate; applying a layer of hot rubberized asphaltbinder; applying a layer of ⅛ inch aggregate that is hot pre-coated with0.5 to 1.0 percent asphalt cement; rolling the ⅛ inch aggregate into therubberized asphalt binder material; allowing the combined binder and ⅛inch aggregate to cure; and removing any loose aggregate.
 2. The methodof claim 1 wherein the polymer modified asphalt rubber binder is appliedat a rate of about 0.60 to 0.70 gallons per square yard.
 3. The methodof claim 1 wherein the ⅜ or ½ inch aggregate is placed at about 28 to 34pounds per square yard.
 4. The method of claim 1 wherein the rubberizedasphalt binder is applied at a rate of about 0.20 to 0.23 gallons persquare yard.
 5. The method of claim 1 wherein the ⅛ inch aggregate isplaced at about 10 to 14 pounds per square yard.
 6. The method of claim1 wherein the polymer modified asphalt rubber binder comprises about 15to 18 percent by weight of reclaimed tire rubber crumb rubber modifierand about 2 percent by weight of SBS polymer, and the rubberized asphaltbinder comprises about 5 to 10 percent by weight of reclaimed tirerubber crumb rubber modifier and about 2 to 4 percent by weight of SBSpolymer.
 7. The method of claim 6 wherein the polymer modified asphaltrubber binder is prepared in a blender unit in which asphalt cement iscombined with crumb rubber modifier and SBS polymer at a temperaturebetween about 375° F. and 450° F., reacted in a distributor truck orreaction vessel at a temperature between about 375° F. and 425° F., andapplied to the pavement at a temperature between about 375° F. and 400°F.
 8. The method of claim 6 wherein the rubberized asphalt binder isprepared in a blender unit in which asphalt cement is combined withcrumb rubber modifier and SBS polymer at a temperature between about375° F. and 450° F., reacted in a distributor truck or reaction vesselat a temperature between about 375° F. and 425° F., and applied to thepavement at a temperature between about 375° F. and 400° F.
 9. A duallayer pavement preservation system comprising a polymer modified asphaltrubber chip seal layer in contact with the pavement; and a rubberizedasphalt binder chip seal layer on top of the polymer modified asphaltrubber chip seal layer.
 10. The system of claim 9 wherein the polymermodified asphalt rubber chip seal layer includes a binder comprisingperformance graded asphalt cement and about 15 to 18 percent by weightof reclaimed tire rubber crumb rubber modifier and about 2 percent byweight of SBS polymer.
 11. The system of claim 10 wherein the rubberizedasphalt binder comprises performance grade asphalt cement and about 5 to10 percent by weight of reclaimed tire rubber crumb rubber modifier andabout 2 to 4 percent by weight of SBS polymer.